Over that time, officials said Friday, 17 men, including 15 employees of the Long Island Rail Road, played a role in what has become a common and lucrative crime: stealing copper, a metal whose value has risen significantly. In this case, the men were accused of taking wire from a rail yard, while on duty; using agency trucks to transport the material to personal vehicles; and selling the wire, for cash, to a local scrap metal company — a routine that netted the group more than $250,000.

“These employees stole from everyone who uses the M.T.A.,” Kathleen M. Rice, the district attorney for Nassau County, said at a news conference.

The 17 defendants were arrested on Friday, in the culmination of an investigation, called Operation Heavy Metal, led by the authority’s inspector general, Barry L. Kluger, who received a tip about the theft last year.

This was not the first illicit scheme at the railroad. Several retired workers have been charged in recent years with federal crimes for falsely claiming to be disabled to collect federal disability pensions — a plot that could have cost the Railroad Retirement Board, which awards disability pensions, more than $1 billion if all of the money had been disbursed.

At the news conference, Helena Williams, the railroad’s president, turned to Mr. Kluger during her remarks. “Barry,” she said, “unfortunately, I speak to you more often than I want to.”

The latest scheme, while smaller in scale, was uncovered at a moment when riders might already have diminishing patience for the transportation authority. The agency remains a long way from repairing all damage sustained during the hurricane, and higher fares and tolls will take effect in March.

The 17 arrests were the culmination of an investigation, called Operation Heavy Metal, led by the Metropolitan Transit Authority's inspector general, Barry L. Kluger, who received a tip about the theft last year.

Uli Seit for The New York Times

“At a time when riders are weeks away from yet another fare increase and budgets are balanced with the narrowest of margins, these thefts are particularly reprehensible,” said Mark Epstein, the chairman of the Long Island Rail Road Commuter Council.

The workers arrested on Friday came from the railroads communication department, officials said, and included two assistant foremen whose annual base salaries were around $80,000. (The remaining workers earned about $65,000 to $70,000 annually, as well as overtime, Mr. Kluger said.)

Investigators said the stolen wire included new spools, severed sections of spools and discarded copper wire that the railroad was gathering to sell for scrap. The price the defendants were paid, Ms. Rice said, depended on whether the wire was new, if it contained lead and if the surrounding plastic coating was stripped away.

The workers have been suspended without pay. Ms. Williams said that if they were convicted, the railroad would fire them and move to terminate their pensions.

She added that the railroad would immediately alter security guidelines to prevent future thefts — increasing video surveillance of yards and shops and providing more secure storage bins on agency grounds.

“There were bins,” Ms. Williams said of the agency’s previous storage accommodations. “Unfortunately, they were open bins.”

Lawyers for some of the workers sought to play down the allegations, arguing that many of the materials in question were of little use to the authority anyway.

Anthony La Pinta, whose client Craig Borsetti is accused of lending his driver’s license to the railroad workers to facilitate sales, said he was flabbergasted by the resources expended to investigate “what many would consider to be the theft and sale of garbage.”

Correction: January 30, 2013

Because of an editing error, an article on Saturday about 15 Long Island Rail Road employees accused of stealing copper from their employer misidentified the official who spoke about the price the defendants were paid for the goods. It was Kathleen M. Rice, the district attorney for Nassau County — not Helena Williams, the railroad’s president.